Due to the exhaust gas specifications for diesel engines becoming stricter, it is necessary to reduce nitric oxides in the exhaust gas. A known possibility consists of reducing the nitric oxides to nitrogen and water in a so-called selective catalytic reduction. This takes place in a so-called SCR catalytic converter while using a reductant injected into the exhaust gas. A water/urea mixture is in particular used for this purpose whose urea decomposes to form ammonia in the exhaust gas which reacts with the nitric oxides. It is important in this process that the exhaust gas is mixed as uniformly as possible with the reductant and that the additive is evaporated as completely as possible to achieve an efficiency which is as large as possible in the reduction.